The conventional wheelchair is comprised of two large diameter, ground engaging, narrow width, pneumatic rear wheels mounted on an axle positioned beneath the seat portion of the chair with smaller diameter, narrow width, pneumatic, ground engaging wheels positioned forwardly of the rear wheels. The front wheels are pivotally mounted to vertical stanchions and generally are not able to be locked in any particular angular position. The occupant of the wheelchair is seated in a conventional fashion such that the lower portion of the occupant's legs will be generally perpendicular to the ground.
The operator of the conventional type wheelchair, when using the wheelchair off-road, is faced with a number of problems. The greatest problem is the instability caused by a high center of gravity. The wheelchair may topple over backwards when negotiating steep grades. When laterally traversing a steep incline, the wheelchair may tip sideways. Furthermore, when traversing downwardly, the occupant risks sliding out of the chair and/or having the chair become unbalanced and having the chair pitch forward.
The conventional wheelchair faces additional difficulties when traversing uneven surfaces or negotiating obstructions in the path. One difficulty is in being unable to proceed any further when a wheel becomes stuck in a depression, such that when the occupant attempts to free himself, the chair may be upset. A similar problem, with the same consequences, occurs when attempting to traverse obstructions--rocks, logs or curbs --in the pathway.
A further problem with the conventional wheelchair is that the user is unable to generate enough sustained human power to climb steep grades. If electric power is used, the battery and transmission make the wheelchair heavy and unwielding. Thus, the conventional wheelchair has limited capability for traversing inclines.
Another type of wheelchair is the sport model. Unlike the conventional model, the occupant's knees are bent upward such that the feet rest nearly in the same plane as the buttocks. The sport model wheelchair typically has a slightly longer wheel base, a slightly lower center of gravity and the hind wheels are slightly wider apart than the regular wheelchair. Sport wheelchairs may or may not have two front pneumatic ground engaging tires which have a tread width wider than the average rear pneumatic wheelchair tire. However, in the sport model, the outside diameter of the rear wheel is usually consistently as large as that of the regular wheelchair.
The sport wheelchair, however, faces problems similar to the conventional wheelchair when utilized off-road and in a steep incline situation. The sport model, while far more stable than the conventional wheelchair, still suffers problems in traversing a steep grade.
Both types of wheelchairs typically use narrow width pneumatic tires which are easily subject to puncture by branches, rocks and the like. When utilized in sandy, loose and unstable soil, the wheels sink and the occupant is stranded.
To lessen the puncture and traction problems several solutions have been propounded. One solution has been to mount an additional rear wheel to each side of the existing rear wheels, or to utilize a metal rear wheel. While the utilization of two adjacent wheels provides better traction, the puncture problem continues to exist and there are still some problems with sinking into soil. The metal wheel, while less likely to sink, lacks traction, and is incredibly uncomfortable for the user.
The wheelchairs of the co-pending applications represented a significant advance in the wheelchair art and solved many of the problems associated with the prior art wheelchairs. The only possible shortcoming to the wheelchairs of the co-pending applications is that it could only be used on land and could not be used on water. The wheelchair disclosed in the instant application is believed to be a significant improvement over the wheelchair described in the co-pending applications in that it may be used in the water and the wheels thereof may be interchanged for the particular type of terrain being traversed.
It is therefore a principal object of the invention to provide an improved all-terrain wheelchair.
Another object of the present invention is to provide a wheelchair which may be utilized on all types of terrain and may be used in water.
Another object of the present invention is to provide a wheelchair having a low center of gravity thereby increasing the stability thereof.
Still another object of the invention is to provide a wheelchair wherein the wheels thereof may be replaced for other types of wheels depending upon the particular terrain being traversed.
Still another object of the invention is to provide a wheelchair of the type described which includes a ratchet arm means at each side thereof for propelling the wheelchair.
Still another object of the invention is to provide an all-terrain wheelchair of the type described which is economical of manufacture, durable in use and refined in appearance.
These and other objects of the present invention will be apparent to those skilled in the art.